JPS6030248B2 - Granulation method of ceramic raw material powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for granulating ceramic raw material powder, and aims to provide a granulated calcined ceramic material suitable for press molding.

In order to obtain a ceramic molded body of a certain shape by press molding, the ceramic raw material powder is granulated in advance.

This granulation process is necessary because it increases the specific gravity of the ceramic granulated powder, lowers the compression ratio of the press to improve formability, and improves the fluidity of the granulated powder when it is fed to the press. This is to increase the Conventionally, methods for granulating ceramic raw material powder include a rolling method, a compression molding method, a spray dryer method, a crystallization method, and an injection method.

Among these, the spray dryer method is said to be the most suitable. In this method, a slurry of ceramic raw material powder uniformly mixed with a water-soluble binder is sprayed from above in a continuous manner, and the droplets are dried and granulated as they fall, making it suitable for mass production. It is often used and is said to have the advantage of easily producing spherical aggregates with good fluidity.

However, it has been pointed out that this method also has the following weaknesses.

1.Drying is almost instantaneous, resulting in hollow granulated particles, making it difficult to obtain particles with high specific gravity.

2. As moisture moves during drying, the fine particles within each particle also move toward the moisture evaporation surface, causing segregation in the particles.

3. Drying the water in slurry requires a large amount of thermal energy, but the processing capacity is relatively low.

In addition, even if slurry is used, the o4 yield is likely to be poor due to the chronology of dry raw materials, and the problem of contamination of impurities occurs when granulating other raw materials. Granulation is restricted.

Therefore, an object of the present invention is to provide a method for granulating ceramic raw material powder for powder press molding, which can improve the above-mentioned drawbacks.

Another object of the present invention is to provide a method for granulating ceramic raw material powder that yields solid, spherical particles.

Another object of the present invention is to provide a dry method for granulating ceramic raw material powder.

That is, the gist of the present invention is to prepare a calcined ceramic raw material powder and a binder that has no bonding force at room temperature and becomes molten when the temperature rises, and to prepare a calcined ceramic raw material powder by A step of generating heat in the calcined ceramic raw material powder, a step of mixing the calcined ceramic raw material powder and a binder, and a step of bringing the calcined ceramic raw material powder in a heat-generating state into contact with the binder melts the binder. This method is characterized by comprising a step of granulating a temporary ceramic raw material powder using a binder containing a powder.

Examples of preliminary ceramic raw material powders include concessionary ceramic raw material powders such as barium titanate-based and strontium titanate-based powders, semiconductor ceramic raw material powders such as barium titanate-based semiconductors and strontium titanate-based semiconductors, or zirconate titanate-based powders. There are piezoelectric ceramic raw material powders such as gold 6 series.

In addition, binders that do not have binding strength at room temperature and become molten when the temperature rises include polyethylene, polypropylene, paraffin wax, microwax, and vinyl resins, and the amount of these added is 10 to 15% by weight. This is the amount necessary for granulation.

Particularly important in this invention is that when mixing the calcined ceramic raw material powder and the binder to obtain the granulated ceramic material, the binder is heated and melted to a molten state;
By mixing the ceramic raw material powder in this state,
Granulated particles with uniform shape and size are obtained.

Specifically, by causing the ceramic raw material powder to generate heat and bringing it into contact with the binder, the binder is melted using the heat generated as a medium. As a heating means for the ceramic raw material powder, the ceramic raw material powder is agitated at high speed, and the frictional heat generated at this time is used to generate heat. To melt the binder, you can add it in advance together with the ceramic raw material powder and melt it by promoting the heat generation of the ceramic raw material powder while simultaneously proceeding with rope mixing, or The raw material powder may be heated and then the binder may be added and mixed. A mixing machine such as a mixer or a blender is used as a means to granulate the raw material powder of Kakeiyo Ceramic.This mixer has a rotating shaft inside and a rope blade is attached to this shaft. In order to generate heat from the raw material powder, the fly azusa blades need to rotate at high speed.

At this time, a suitable value for the speed of the thick floating blade is a circumferential speed of 20 to 40 m/sec.

The present invention will be described in detail below based on examples.

A barium titanate-based ceramic raw material powder for dielectric ceramics was prepared as a calcined ceramic raw material powder.

At this time, the average particle size of the raw material powder was 1.80 grains. Next, 1.5 [9] of this raw material powder was put into a mixer and heated to heat the raw material powder to the melting temperature of the binder. Furthermore, various powdered or granular binders shown in Table 1 were added to the tank of the mixer, and granulated by rope mixing. The obtained granulated particles were cooled, and the powder characteristics of each particle were measured. As powder characteristics, bulk specific gravity, flow rate, average particle size, and particle shape were measured. Table 1 also shows the measurement results of high specific gravity and flow rate. Note that the flow rate indicates the time it takes for 30 samples to pass through a funnel tube with a diameter of 9 mm and a total length of 8 mm from the input port to the discharge port. This flow rate is a guideline for determining the fluidity when feeding the granulated ceramic raw powder to the powder press machine.If the fluidity is good, the raw powder can be fed smoothly and workability can be improved. . As a reference example, the powder properties of ceramic raw material powder granulated using the spray dryer method were similarly measured, and the measurement results are shown in Table 1.

Table 1 It was also confirmed that the average particle size of the granulated particles obtained by the method of this invention was 150 to 300 mesh, and that the particle shape was solid and nearly spherical.

From the above, the method according to the present invention shows superior results in various properties, such as higher specific gravity and faster flow rate than the spray method.
Next, the obtained granulated calcined ceramic raw material powder was molded and fired, and the conditions at each step were observed.

In the molding process, pressure was applied using a 5-ton press to a point where the molding specific gravity could be increased, and the molding specific gravity was measured. As a result, conventional spray dryer products have a molding specific gravity of 3.
The maximum value was 4, but for the products according to the present invention (sample numbers 1 to 4), it was possible to increase the value to 3.7. Furthermore, no ceramic raw powder was observed to adhere to the mold. The reason why the molding specific gravity is higher than that of conventional products is that the binder uniformly coated on the particle surface by granulation plays the role of an anti-friction agent, helping the movement of each particle when pressurized. This is thought to be possible.

This is largely related to the fact that the binder is based on a thermoplastic resin or wax, and the amount of binder is somewhat large, and exhibits a behavior different from that of conventional cedar-soluble/binder. Furthermore, the molded body was fired in air at 1300 oo for 1 hour, and the surface and internal pores of the Akatsuki compact were examined, and the results showed that the number of pores could be reduced compared to the conventional method.

As described above, according to the granulation method of the present invention, since water is not used,
The process can be simplified, and heating energy for removing moisture, unlike when using a spray dryer method, is not required, contributing to energy savings.

Claims (1)

[Claims] 1. A step of preparing calcined ceramic raw material powder and a binder that has no bonding strength at room temperature and becomes molten when the temperature rises, and calcination by stirring the calcined ceramic raw material powder. a step of generating heat in the ceramic raw material powder; a step of mixing the calcined ceramic raw material powder and a binder;
Granulation of ceramic raw material powder comprising the steps of: bringing the calcined ceramic raw material powder in an exothermic state into contact with the binder to melt the binder, and granulating the calcined ceramic raw material powder with the molten binder; Law. 2. Claim 1, characterized in that the mixing step is performed after the step of generating heat for the calcined ceramic raw material powder.
A method for granulating ceramic raw material powder as described in Section 1. 3. A method for granulating ceramic raw material powder according to claim 1, characterized in that the step of granulating the calcined ceramic raw material powder is carried out while the step of generating heat and the mixing step are performed simultaneously.